Tabby's star is dimming at an incredible rate • Hacker News Board

Re: Tabby's star is dimming at an incredible rate

#141

Post by cstross » Sun, Aug 07, 2016, 1:04 PM UTC

e12e wrote: post #138

peonicles wrote: post #59

Earlier quoted context omitted.

There's a comment [1] in the other reddit thread that somewhat rules this out. > That doesn't even make sense when you're flying within the Solar System. Stuff moves, so you have to fly towards where it's going to be, not where it is. > The star is far enough away to be treated as a point source, with its light forming an apparent cone with the Earth's diameter. It doesn't intuitively make sense, at least to me, that…

Unless military tactics dictate that they try to "hide" in the cone since they first picked up our radio signals... Even If they're on a "civilian" mission, they might have navigators/a captain with military training...

Not plausible because:

a) Tabby's Star is roughly 1500 light years away from us; we only began emitting radio signals ~150 years ago (at most -- assuming propagation from early telegraph wires; not actually very likely) and it'd take ~3000 years for our signals to reach the vicinity of Tabby's Star and indications of a reaction getting back to us,

b) "Military" is a category error on this scale; the energy budget required to generate the sort of luminosity changes we're seeing around Tabby's Star by deliberately occulting it are mind-blowing compared to anything we've ever achieved. Might as well speculate about an ant-hill (us) wondering about the military intentions of an M1 Abrams tank driving across the Iraqi desert (hypothetical alien actors at Tabby's star) -- either they aren't going to drive over us, or we just encountered an Outside Context Problem.

Re: Tabby's star is dimming at an incredible rate

#142

Post by quantumhobbit » Sun, Aug 07, 2016, 1:06 PM UTC

raverbashing wrote: post #131

monort wrote: post #126

Earlier quoted context omitted.

You can you use a giant mirror, that directs light to your ship's sail.

I really wonder what would happen if you really had a giant mirror reflecting all the Sun's energy back to itself

It would increase the sun's temperature causing it to expand. I guess eventually it would expand out to reach your dyson mirror.

Of course there would be all sorts of secondary effects, lowering the density in the core could slow down the rate of fusion, increased temp would increase it, but no garuntee that the effects would cancel. Also depending on how far out your mirror is the core might not ever notice the change. The outer layers could heat up and destroy your mirror before the increased temperature reaches the core.

Re: Tabby's star is dimming at an incredible rate

#143

Post by quantumhobbit » Sun, Aug 07, 2016, 1:11 PM UTC

yoodenvranx wrote: post #76

whage wrote: post #58

Earlier quoted context omitted.

Do spaceships travel in a straight line? I thought their trajectories are heavily curved in really weird ways due to the garvities of stars and planets around them. Please enlighten me!

I think you overestimate the density of stars in the universe. If I remember correctly there are typically a few lightyears between each star (on average).

There would still be a curved orbit around the center of the galaxy. That is a bit like arguing that a mission from Earth to Mars would travel in a straight line because there isn't anything in between them.

Re: Tabby's star is dimming at an incredible rate

#144

Post by ceejayoz » Sun, Aug 07, 2016, 1:27 PM UTC

roberthahn wrote: post #114

The dimming is probably a dark matter nebula passing between it and us.

https://en.wikipedia.org/wiki/Dark_matter

> The name refers to the fact that it does not emit or interact with electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum.

Re: Tabby's star is dimming at an incredible rate

#145

Post by SolarNet » Sun, Aug 07, 2016, 1:28 PM UTC

phyzome wrote: post #105

lucb1e wrote: post #20

Earlier quoted context omitted.

Well whatever it is, we probably have 1000+ years to save ourselves right? If whatever caused it comes at us at 50% light speed, which sounds unlikely given how fast that already is, we'd still have 700 years. I'm pretty sure that if human's resources were suddenly all turned towards getting the hell out of here, we could certainly pull it off for a good part of the population in a few hundred years. Whether we'd eve…

700 years would be twice light speed; at 0.5c it would be 3000 years.

The math is wrong but not quite in the way you figure it. His point was that if the spaceship launched at the same time as the light left and the spaceship was traveling at 0.5c. So it would be 1480 years again (1/0.5 * 1480 - 1/1 * 1480).

Re: Tabby's star is dimming at an incredible rate

#146

Post by JumpCrisscross » Sun, Aug 07, 2016, 1:35 PM UTC

Zardoz84 wrote: post #74

erdevs wrote: post #68

Good ol' PV on Kinja (from the linked gizmodo article: http://gizmodo.com/the-so-called-alien-megastructure-just-go... ) has some interesting thoughts, as usual. > The biggest axe against it being an alien megastructure project is the fact its an F-type star. F-types only live a couple billion years, depending on mass. > But the drop in the radiant flux... a sustained drop. That could be something far more interestin…

Spectral type isn't 1-1 correlate with the star estimated life. Depends on the star mass. Our Sun was one time a F type star.

Do we have a "longevity" estimate for Tabby's star?

By estimating how much starlifting would explain the observed luminosity drop, and then backing out the expected increase in the star's life against its flux decrease one could estimate how efficient the "aliens'" energy-harvesting technology is (coupled to a financial discount rate).

Re: Tabby's star is dimming at an incredible rate

#147

Post by sitkack » Sun, Aug 07, 2016, 1:53 PM UTC

e12e wrote: post #137

tzs wrote: post #130

Earlier quoted context omitted.

If I'm doing that math right, it works out that to not be ruled out by parallax, the object would have to be almost 2 AU in diameter if it was within a few light years of Earth. That seems pretty ridiculous--now we have them not only building a megastructure, but flying it to Earth! However, I wonder if there is a way to save the idea without requiring a ridiculously large spacecraft? Suppose instead of one ginormous…

Maybe the visible size of the ship is bigger, as it's unfolding / building a solar sail to brake using our sun's radiation? (like a parachute on a drag racer). Ah, but 2au is probably still way too big?

What if the parachute was a big magnetically contained gas cloud ?

Re: Tabby's star is dimming at an incredible rate

#148

Post by e12e » Sun, Aug 07, 2016, 2:06 PM UTC

cstross wrote: post #141

e12e wrote: post #138

Earlier quoted context omitted.

Unless military tactics dictate that they try to "hide" in the cone since they first picked up our radio signals... Even If they're on a "civilian" mission, they might have navigators/a captain with military training...

Not plausible because: a) Tabby's Star is roughly 1500 light years away from us; we only began emitting radio signals ~150 years ago (at most -- assuming propagation from early telegraph wires; not actually very likely) and it'd take ~3000 years for our signals to reach the vicinity of Tabby's Star and indications of a reaction getting back to us, b) "Military" is a category error on this scale; the energy budget req…

A) but if the ship is only 2 ly away, they could've changed maneuvering a hundred years ago.

B) sure.

Re: Tabby's star is dimming at an incredible rate

#149

Post by Symmetry » Sun, Aug 07, 2016, 2:22 PM UTC

jerf wrote: post #22

lucb1e wrote: post #20

Earlier quoted context omitted.

Well whatever it is, we probably have 1000+ years to save ourselves right? If whatever caused it comes at us at 50% light speed, which sounds unlikely given how fast that already is, we'd still have 700 years. I'm pretty sure that if human's resources were suddenly all turned towards getting the hell out of here, we could certainly pull it off for a good part of the population in a few hundred years. Whether we'd eve…

"Well whatever it is, we probably have 1000+ years to save ourselves right?" No. That time has already passed. If we see signs that the star will go nova "in one year", we have one year, not 1481. The popular idea that we see "the past" in the sky is not really the best way to think about it. It is far more accurate to say that there is no such thing as "the" present, and what we see in the sky really is our present.…

Yeah, it looks like a supernova 1500 ly away might produce enough gamma rays that we could actually measure their effect on the ozone layer but not enough that it would be concerning.

https://en.wikipedia.org/wiki/Near-Earth_supernova

Unexplained dimmings do give rise to the question of "Is it about to explode" but we have a good sense of how often large explosions occur in galaxies because they're so obvious and so I suppose I shouldn't be concerned about natural phenomenon. And given the potential expansion rates of being who could create megastructures like this our priors on that explanation have to be pretty low.

Re: Tabby's star is dimming at an incredible rate

#150

Post by Symmetry » Sun, Aug 07, 2016, 2:30 PM UTC

int_19h wrote: post #128

mkstowegnv wrote: post #110

Earlier quoted context omitted.

IMHO the aliens will not be specifically seeking life that is intelligent. Singularities and interstellar traveling alien civilizations share a problem. If one is in essence immortal the only purpose that can endure forever is the pursuit of new knowledge. Even if alien entities are able to learn all there is to know about all the other sciences, biology will be inexhaustible as the novel patterns that can be produce…

>> biology will be inexhaustible as the novel patterns that can be produced by evolution are effectively infinite But why do you assume they would be interested in observing the patterns that actually have been produced, instead of running high-precision evolutionary emulators that can generate patterns that could be produced at a much higher rate, and maybe even some automated filters to condense it down to "interes…

Thermodynamics still limits what you can compute and, given the output of a single star, you're still limited in what can be computed.

But I think it's a mistake to try to characterize any civilization by a single motivation. People on Earth do things for many different reasons and I think we should expect the same of alien civilizations even if single motivations tax our imaginations less. The questions is if any of the motivations driving a stellar civilization would be enough to prompt the establishment of colonies. I don't think you can say that the answer will be 'no' reliably for every civilization that might arise and it only takes on to colonize a galaxy in short order (by cosmic standards). Hence sophisticated life is probably very rare.